Polyaxial bone screw assembly with fixed retaining structure

ABSTRACT

A polyaxial bone screw assembly includes a threaded shank body having an integral upper portion receivable in a receiver and retained within the receiver by a retaining structure in the form of an open ring. The receiver has a U-shaped channel for receiving a spinal fixation rod. The shank upper portion is designed to directly frictionally engage the spinal fixation rod when a closure structure operably urges the rod toward the upper portion, fixing the bone screw shank body in a selected angular orientation with respect to the receiver.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.60/699,092 filed Jul. 14, 2005. The present application is acontinuation-in-part of U.S. patent application Ser. No. 10/818,554,filed Apr. 5, 2004, now U.S. Pat. No. 7,662,175, which was acontinuation of U.S. patent application Ser. No. 10/464,633, filed Jun.18, 2003, now U.S. Pat. No. 6,716,214 and a continuation-in-part of U.S.patent application Ser. No. 10/651,003, filed Aug. 28, 2003, now U.S.Pat. No. 8,137,386.

BACKGROUND OF THE INVENTION

The present invention is directed to polyaxial bone screws for use inbone surgery, particularly spinal surgery. Such screws have a rodreceiver that can swivel about a shank of the bone screw, allowing thereceiver to be positioned in any of a number of angular configurationsrelative to the shank.

Many spinal surgery procedures require securing various implants to boneand especially to vertebrae along the spine. For example, elongate rodsare often utilized that extend along the spine to provide support tovertebrae that have been damaged or weakened due to injury or disease.Such rods must be supported by certain vertebrae and support othervertebrae.

The most common mechanism for providing vertebral support is to implantbone screws into certain bones which then in turn support the rod or aresupported by the rod. Bone screws of this type may have a fixed head orreceiver relative to a shank thereof. In the fixed bone screws, thereceiver cannot be moved relative to the shank and the rod must befavorably positioned in order for it to be placed within the receiver.This is sometimes very difficult or impossible to do. Therefore,polyaxial bone screws are commonly preferred.

Polyaxial bone screws allow rotation of the receiver about the shankuntil a desired rotational position of the receiver is achieved relativeto the shank. Thereafter, a rod can be inserted into the receiver andeventually the receiver is locked or fixed in a particular positionrelative to the shank.

A variety of polyaxial or swivel-head bone screw assemblies areavailable. One type of bone screw assembly includes an open receiverthat allows for placement of a rod within the receiver. A closure top orplug is then used to capture the rod in the receiver of the screw.

Because such implants are for placement within the human body, it isdesirable for the implant to have as little effect on the body aspossible. Consequently, heavy, bulky implants are undesirable andlighter implants with a relatively small profile both in height andwidth are more desirable. However, a drawback to smaller, lighterimplants is that they may be more difficult to rigidly fix to each otherand into a desired angular position. Lack of bulk may also mean lack ofstrength, resulting in slippage under high loading. Also, more componentparts may be required to rigidly fix the implant in a desired position.A further drawback of smaller components is that they may be difficultto handle during surgery because of their small size or fail to provideadequate driving or gripping surfaces for tools used to drive the shankinto bone or drive the closure top into the screw head.

SUMMARY OF THE INVENTION

A polyaxial bone screw assembly of the present invention includes ashank having a body for fixation to a bone and an upper portionreceivable in a cavity of a receiver. A retaining structure, preferablya collar-like retaining ring is also receivable in the cavity. Theretaining structure is resilient and open, including first and secondspaced ends being movable toward and away from one another. The shankupper portion and the retaining structure are sized and shaped to bebottom loadable into the receiver, with the retaining structure beingcompressed during insertion. Upon expanding to an original form, theretaining structure engages the receiver and captures the shank upperportion within a cavity of the receiver.

Another aspect of the invention is a tool engagement formation on theshank upper portion, allowing for non-slip engagement by a tool fordriving the bone screw shank into bone. The tool engagement formationmay be in the form of an axial projection or an internal drive. Theillustrated receiver includes an open channel communicating with thecavity that receives the shank upper portion and the retainingstructure. The channel is sized and shaped for receiving a rod or otherstructural member and includes arms with a discontinuous guide andadvancement structure for mating with a guide and advancement structureof a closure structure. The guide and advancement structure ispreferably a flange form or other splay resistant guide and advancementstructure. The shank upper portion is sized and shaped for frictionalcontact with a rod seated in the channel. In operation, a closurestructure operably urges the rod into direct contact with the upperportion of the bone screw shank which in turn frictionally engages theretaining structure, fixing the bone screw shank body in a selectedangular orientation with respect to the receiver.

OBJECTS AND ADVANTAGES OF THE INVENTION

Therefore, objects of the present invention include providing apolyaxial bone screw assembly with features that may be readily,securely fastened to each other and to bone. Furthermore, it is anobject of the invention to provide a lightweight, low profile polyaxialbone screw assembly that may be assembled prior to implantation and alsoassembles in such a manner that the components cooperate to create anoverall structure that prevents unintentional disassembly. Anotherobject of the invention is to provide a polyaxial bone screw assemblywith a reduced number of components; specifically a bone screw assemblythat does not require spacers, compression transfer members or otherinserts for placement between a rod and the bone screw shank portioncaptured within the receiver. A further object of the invention is toprovide a polyaxial bone screw assembly that is relatively easy to use,inexpensive to produce and especially well adapted for the intendedusage thereof.

Other objects and advantages of the invention will become apparent fromthe following description taken in conjunction with the accompanyingdrawings wherein are set forth, by way of illustration and example,certain embodiments of this invention. The drawings constitute a part ofthis specification and include exemplary embodiments of the presentinvention and illustrate various objects and features thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view of a polyaxial bone screwassembly according to the present invention having a shank, a receiver,and a retaining structure, and shown with a rod and a closure structure.

FIG. 2 is an enlarged top plan view of the retaining structure of FIG.1.

FIG. 3 is a cross-sectional view taken along the line 3-3 of FIG. 2.

FIG. 4 is an enlarged cross-sectional view of the receiver, taken alongthe line 4-4 of FIG. 1.

FIG. 5 is an enlarged front elevational view of the shank of FIG. 1.

FIG. 6 is a cross-sectional view taken along the line 6-6 of FIG. 5.

FIG. 7 is an enlarged top plan view of the shank of FIG. 5.

FIG. 8 is an enlarged partial front elevational view of the shank ofFIG. 1 shown fully assembled with the retaining structure, receiver, rodand closure structure of FIG. 1, with portions broken away to show thedetail thereof.

FIG. 9 is a partial front elevational view with portions broken awaysimilar to FIG. 8, showing an articulation of the shank with respect tothe receiver.

FIG. 10 is a partial perspective view, showing the shank, receiver,retaining structure, rod and closure structure of FIG. 1 fully assembledand implanted in a vertebra, shown in cross-section.

FIG. 11 is an exploded perspective view of a second embodiment of apolyaxial bone screw assembly according to the present invention havinga shank, a receiver, and a retaining structure, and shown with a rod anda closure structure.

FIG. 12 is an enlarged front elevational view of the shank of FIG. 11.

FIG. 13 is a cross-sectional view taken along the line 13-13 of FIG. 12.

FIG. 14 is an enlarged top plan view of the shank of FIG. 12.

FIG. 15 is an enlarged partial front elevational view of the shank ofFIG. 11 shown fully assembled with the retaining structure, receiver,rod and closure structure of FIG. 11, with portions broken away to showthe detail thereof.

FIG. 16 is a partial front elevational view with portions broken awaysimilar to FIG. 15, showing an articulation of the shank with respect tothe receiver.

FIG. 17 is a partial perspective view, showing the shank, receiver,retaining structure, rod and closure structure of FIG. 11 fullyassembled and implanted in a vertebra, shown in cross-section.

FIG. 18 is an exploded perspective view of a third embodiment of apolyaxial bone screw assembly according to the present invention havinga shank, a receiver, and a retaining structure, and shown with a rod anda closure structure.

FIG. 19 is an enlarged top plan view of the retaining structure of FIG.18.

FIG. 20 is a cross-sectional view taken along the line 20-20 of FIG. 19.

FIG. 21 is an enlarged cross-sectional view of the receiver, taken alongthe line 21-21 of FIG. 18.

FIG. 22 is an enlarged front elevational view of the shank of FIG. 18.

FIG. 23 is a cross-sectional view taken along the line 23-23 of FIG. 22.

FIG. 24 is an enlarged top plan view of the shank of FIG. 22.

FIG. 25 is an enlarged partial front elevational view of the shank ofFIG. 18 shown fully assembled with the retaining structure, receiver,rod and closure structure of FIG. 18, with portions broken away to showthe detail thereof.

FIG. 26 is a partial front elevational view with portions broken awaysimilar to FIG. 25, showing an articulation of the shank with respect tothe receiver.

FIG. 27 is a partial perspective view, showing the shank, receiver,retaining structure, rod and closure structure of FIG. 18 fullyassembled and implanted in a vertebra, shown in cross-section.

FIG. 28 is an exploded perspective view of a fourth embodiment of apolyaxial bone screw assembly according to the present invention havinga shank, a receiver, and a retaining structure, and shown with a rod anda closure structure.

FIG. 29 is an enlarged front elevational view of the shank of FIG. 28.

FIG. 30 is a cross-sectional view taken along the line 30-30 of FIG. 29.

FIG. 31 is an enlarged top plan view of the shank of FIG. 29.

FIG. 32 is an enlarged partial front elevational view of the shank ofFIG. 28 shown fully assembled with the retaining structure, receiver,rod and closure structure of FIG. 28, with portions broken away to showthe detail thereof.

FIG. 33 is a partial front elevational view with portions broken awaysimilar to FIG. 32, showing an articulation of the shank with respect tothe receiver.

DETAILED DESCRIPTION OF THE INVENTION

As required, detailed embodiments of the present invention are disclosedherein; however, it is to be understood that the disclosed embodimentsare merely exemplary of the invention, which may be embodied in variousforms. Therefore, specific structural and functional details disclosedherein are not to be interpreted as limiting, but merely as a basis forthe claims and as a representative basis for teaching one skilled in theart to variously employ the present invention in virtually anyappropriately detailed structure.

With reference to FIGS. 1-10, the reference numeral 1 generallyrepresents a polyaxial bone screw assembly according to the presentinvention. The assembly 1 includes a shank 4 that further includes abody 6 integral with an upwardly extending upper portion or capturestructure 8; a receiver 10; and an independent open retaining structure12. The shank 4, the receiver 10 and the retaining structure 12preferably are assembled prior to implantation of the shank body 6 intoa vertebra 15.

FIGS. 1 and 8-10 further show a closure structure 18 for compressing andbiasing a longitudinal member such as a rod 21 against the shank upperportion 8 biasing the upper portion 8 into fixed frictional contact withthe retaining structure 12 installed in the receiver 10, so as to fixthe rod 21 relative to the vertebra 15. The receiver 10, the retainingstructure 12 and the shank 4 cooperate in such a manner that thereceiver 10 and the shank 4 can be secured at any of a plurality ofangles, articulations or rotational alignments relative to one anotherand within a selected range of angles both from side to side and fromfront to rear, to enable flexible or articulated engagement of thereceiver 10 with the shank 4 until both are locked or fixed relative toeach other near an end of an implantation procedure.

The shank 4, best illustrated in FIGS. 1 and 5-7, is elongate, with theshank body 6 having a helically wound bone implantable thread 24extending from near a neck 26 located adjacent to the capture structure8 to a tip 28 of the body 6 and extending radially outwardly therefrom.During use, the body 6 utilizing the thread 24 for gripping andadvancement is implanted into the vertebra 15 leading with the tip 28and driven down into the vertebra 15 with an installation or drivingtool (not shown), so as to be implanted in the vertebra 15 to near theneck 26, as shown in FIG. 10, and as is described more fully in theparagraphs below. The shank 4 has an elongate axis of rotation generallyidentified by the reference letter A. It is noted that any reference tothe words top, bottom, up and down, and the like, in this applicationrefers to the alignment shown in the various drawings, as well as thenormal connotations applied to such devices, and is not intended torestrict positioning of the assembly 1 in actual use.

The neck 26 extends axially outwardly and upwardly from the shank body6. With particular reference to FIGS. 5 and 6, the illustrated neck 26is of reduced radius as compared to the shank body 6 and an outerdiameter of the thread 24. Further extending axially and outwardly fromthe neck 26 is the shank upper portion 8 that provides a connective orcapture structure disposed at a distance from the thread 24 and thus ata distance from the vertebra 15 when the body 6 is implanted in thevertebra 15.

The shank upper portion 8 is configured for connecting the shank 4 tothe receiver 10 and capturing the shank 4 in the receiver 10. Withparticular reference to FIGS. 1 and 5-7, the upper portion 8 has anouter, convex and partially spherical or hemispherical surface 34 thatextends outwardly and upwardly from the neck 26 and terminates at asubstantially annular surface 38. The spherical surface 34 has an outerradius configured for sliding cooperation and ultimate frictional matingwith a concave surface of the retaining structure 12 and a partiallyspherical inner surface of the receiver 10, having a substantiallysimilar radius, discussed more fully in the paragraphs below. The flatsurface 38 is substantially perpendicular to the axis A. The sphericalsurface 34 shown in the present embodiment is smooth, but it is foreseenthat such surface may include a roughened or textured surface or surfacefinish, or may be scored, knurled, or the like, for enhancing frictionalengagement with the retaining structure 12 and the receiver 10. Acounter sunk substantially planar base or seating surface 40 also isdisposed perpendicular to the axis A and extends radially from acentrally located tool engagement structure 41. The sunken seatingsurface 40 is disposed between the tool engagement structure and thesurface 38. The structure 41 has a top 42 and six driving faces 43 thatform a hexagonal extension head driving structure mateable with a socketdriving tool (not shown). The base 40 also includes a hexagonal outerperimeter 44 defined by outer driving faces that are parallel to theaxis A and terminate at the surface 38. The tool engagement structure 41is coaxial with the bone screw body 6 and extends along the axis A. Inoperation, a driving tool (not shown) fits about and engages the toolengagement structure 41 at the faces 43 for both driving and rotatingthe shank body 6 into the vertebra 15. A bottom of the driving tool mayabut against the base 40 and also the faces defining the outer hexagonalperimeter 44, providing additional surfaces for engagement with thedriving tool. It is foreseen that in other embodiments according to theinvention, the driving features of the bone screw shank may take avariety of forms, including internal and external drives of differentshapes and sized. As will be described with respect to the bone screwassembly 601 below, in smaller embodiments, a curved, concave surfacemay extend from the tool engagement structure to the outer sphericalsurface, allowing for the tool engagement structure to be designed witha somewhat longer axial length and thus providing a greater surface areafor engagement with a driving tool, but without the planar seatingsurface 40 and additional planar driving faces because of the limitationof the small size of such a bone screw.

The top end surface 42 of the shank 4 is preferably curved ordome-shaped as shown in the drawings, for simple smooth contactengagement or positive mating engagement with the rod 21, when the bonescrew assembly 1 is assembled, as shown in FIGS. 8 and 9 and in anyangular arrangement of the shank 4 relative to the receiver 10. In theillustrated embodiment the surface 42 is smooth. While not required inaccordance with the practice of the invention, the surface 42 may bescored, knurled or the like to further increase frictional positivemating engagement between the surface 42 and the rod 21.

The shank 4 shown in the drawings is cannulated, having a small centralbore 45 extending an entire length of the shank 4 along the axis A,coaxial with the threaded body 6. The bore 45 has a first circularopening 46 at the shank tip 28 and a second circular opening 48 at thetop surface 42. The bore 45 provides a passage through the shank 4interior for a length of wire (not shown) inserted into the vertebra 15prior to the insertion of the shank body 6, the wire providing a guidefor insertion of the shank body 6 into the vertebra 15.

Referring to FIGS. 1 and 4, the receiver 10 has a generally U-shapedappearance with a discontinuous partially cylindrical inner profile anda faceted outer profile. The receiver 10 includes a base 50 integralwith a pair of upstanding arms 52 and 54 forming a U-shaped cradle anddefining a U-shaped channel 56 between the arms 52 and 54 with an upperopening 57 and a lower seat 58 having substantially the same radius asthe rod 21 for operably snugly receiving the rod 21.

Each of the arms 52 and 54 has an interior surface 60 that in partdefines the inner cylindrical profile and includes a partial helicallywound guide and advancement structure 62 having an axis of rotation B.In the illustrated embodiment, the guide and advancement structure 62 isa partial helically wound interlocking flangeform configured to mateunder rotation with a similar structure on the closure structure 18, asdescribed more fully below. However, it is foreseen that the guide andadvancement structure 62 could alternatively be another type of splaypreventing structure such as a buttress thread, a square thread, areverse angle thread or other thread like or non-thread like helicallywound discontinuous advancement structure for operably guiding underrotation and advancing the closure structure 18 downward between thearms 52 and 54, as well as eventual torquing when the closure structure18 abuts against the rod 21.

Tool engaging apertures or grip bores 64 are formed within the arms 52and 54 and may be used for holding the receiver 10 during assembly withthe shank 4 and the retaining structure 12 and also during theimplantation of the shank body 6 into a vertebra 15. A holding tool (notshown) and the apertures 64 can be configured for a snap on/spring off,snap on/twist off, twist on/twist off, twist on/pry off or otherflexible engagement wherein the holding tool has flexible legs whichsplay outwardly to position the tool for engagement in the apertures 64.It is noted that the apertures 64 the cooperating holding tool may beconfigured to be of a variety of sizes and locations along any of thesurfaces of the arms 52 and 54. In the illustrated embodiment, theapertures 64 communicate with upwardly projecting hidden recesses 66 tofurther aid in securely holding the receiver 10 to a holding tool.

Communicating with and located beneath the U-shaped channel 56 of thereceiver 10 is a chamber or cavity 78 substantially defined by an inner,substantially spherical or partially cylindrical surface 80 of the base50 and an inner substantially spherical concave surface 82 thatcommunicates with the U-shaped channel 56. The spherical surface 82 isdisposed between the channel 56 and the inner surface 80. Acircumferential ridge 83 is formed at the intersection of the innersurface 60 and the inner substantially spherical surface 82. Thesubstantially spherical surface 82 is sized and shaped for slidablemating and eventual frictional engagement with the shank upper portion8, having a radius that is approximately the same as a radius of theconvex surface 34 of the shank upper portion 8 as described more fullybelow. The concave spherical surface 82 opens or widens at the lowersurface 80, the surface 80 being sized to receive a shank upper portion8 bottom loaded at a lower opening 84 of the receiver 10 where thesurface 80 opens to an exterior 85 of the base 50. It is foreseen thatif desired, some of the lower surface 80 may be cylindrical in nature(similar to the surface 280 of the assembly 201), rather than partiallyspherical as shown in FIG. 4. The spherical surface 82 provides a stop,upper shoulder or barrier near and at the ridge 83 prohibiting the shankupper portion 8 from being removable through the channel 56. The lowerinner surface that opens to the exterior 85 of the base 50 is coaxiallyaligned with respect to the rotational axis B of the receiver 10 and issized and shaped to receive the shank upper portion 8 therethrough andalso receive the retaining structure 12 when the structure 12 is in acompressed configuration as will be described in greater detail below.Formed in a portion of the surface 80 near the spherical inner surface82 is a circumferential recess or groove 86 that is sized and shaped toreceive the retaining structure 12 when the structure 12 is in anuncompressed position as will also be discussed further below, so as toform a restriction at the location of the groove 86 to prevent theuncompressed retaining structure 12 from passing from the cavity 78 andout the lower opening 84 of the receiver 10 when the retaining structure12 is loaded and seated in the groove 86, thereby also retaining theshank upper portion 8 within the cavity 78. Between the groove 86 andthe opening 84 communicating with the base exterior 85, the receiverincludes a chamfer or conical surface 88. As illustrated in FIG. 9, thesurface 88 provides additional clearance for an angled or articulatedbone screw shank 4 with respect to the receiver 10.

The retaining structure or collar 12 that is used to retain the capturestructure 8 of the shank 4 within the receiver 10 is best illustrated byFIGS. 1-3. The structure 12 has a central axis C that is operationallythe same as the axis B associated with the receiver 10 when the capturestructure 8 and the retaining structure 12 are installed within thereceiver 10. The retaining structure 12 has a central channel or hollow91 that passes entirely through the structure 12 from a top surface 92to a bottom surface 94 thereof. Surfaces that define the channel 91include a discontinuous inner spherical surface 95 adjacent the topsurface 92; an edge 97 adjacent the surface 95 and coaxial with the axisC; and a discontinuous conical surface, bevel or chamfer 98 sloping awayfrom the axis C, adjacent the edge 97 and terminating at the bottomsurface 94. The spherical surface 95 has a radius sized and shaped tocooperate with a radius of the substantially spherical surface 34 of theshank upper portion 8 such that the surface 95 slidingly and pivotallymates with the spherical surface 34 as described more fully below. Thesurface 95 may include a roughening or surface finish for providingadditional frictional contact between the surface 95 and the surface 34,once a desired angle of articulation of the shank 4 with respect to thereceiver 10 is reached.

The resilient retaining structure 12 includes first and second endsurfaces, 100 and 101 disposed in spaced relation to one another and anouter substantially cylindrical surface 104. Both end surfaces 100 and101 are disposed substantially perpendicular to the top surface 92 andthe bottom surface 94. A width X between the surfaces 100 and 101 isdetermined by a desired amount of compressibility of the open retainingstructure 12 when loaded into the receiver 10. The space X shown in FIG.2 provides adequate space between the surfaces 100 and 101 for theretaining structure 12 to be pinched, with the surfaces 100 and 101compressed toward one another to an almost touching or touchingconfiguration, to an extent that the compressed retaining structure 12is up or bottom loadable through the opening 84. After passing throughthe opening 84 and along a portion of the lower inner surface, theretaining structure 12 expands or springs back to an originaluncompressed, rounded or collar-like configuration of FIG. 2 once in thegroove 86. The embodiment shown in FIG. 2 illustrates the surfaces 100and 101 as substantially parallel and vertical, however, it is foreseenthat it may be desirable to orient the surfaces obliquely or at a slightangle depending upon the amount of compression desired during loading ofthe retaining and articulating structure 12 into the receiver 10.

FIGS. 8 and 9 illustrate the structure 12 installed in the groove 86 ofthe receiver 10 and in engagement with the shank upper portion 8. FIG. 8illustrates the shank 4, receiver 10 and retaining structure 12 inco-axial alignment. In other words, axes A, B and C are aligned. FIG. 9illustrates an articulating or swiveling relationship between the upperportion 8 and the installed retaining structure 12 wherein the bonescrew upper portion 8 is slidable with respect to the retainingstructure 12 at the surface 95, resulting in an orientation wherein theaxis A of the shank 4 is not axially aligned with, but rather disposedat an angle with respect to the axes B and C of the receiver 10 and theretaining structure 12 respectively.

The elongate rod or longitudinal member 21 that is utilized with theassembly 1 can be any of a variety of implants utilized inreconstructive spinal surgery, but is normally a cylindrical elongatestructure having a smooth cylindrical surface 116 of uniform diameter.The rod 21 is preferably sized and shaped to snugly seat near the bottomof the U-shaped channel 56 of the receiver 10 and, during normaloperation, is positioned slightly above the bottom of the channel 56 atthe lower seat 58. In particular, the rod 21 normally directly orabutingly engages the shank top surface 42, as shown in FIGS. 8 and 9and is biased against the domed shank top surface 42, consequentlybiasing the shank 4 downwardly in a direction toward the base 50 of thereceiver 10 when the assembly 1 is fully assembled. For this to occur,the shank top surface 42 must extend at least slightly into the space ofthe channel 56 when engaging the retaining structure 12. The shank 4 isthereby locked or held in position relative to the receiver 10 by therod 21 firmly pushing downward on the shank top surface 42.

With reference to FIGS. 1 and 8-10, the closure structure or closure top18 can be any of a variety of different types of closure structures foruse in conjunction with the present invention with suitable matingstructure on the upstanding arms 52 and 54. In the embodiment shown, theclosure top 18 is rotatably received between the spaced arms 52 and 54.It is foreseen that a mating and advancement structure could be locatedon the external surfaces of the arms 52 and 54 for mating with a closuretop.

The illustrated closure top 18 has a generally cylindrical shaped base128 with an upwardly extending break-off head 130. The base 128 includesa helically wound guide and advancement structure 131 that is sized,shaped and positioned so as to engage the guide and advancementstructure 62 on the arms 52 and 54 to provide for rotating advancementof the closure structure 18 into the receiver 10 when rotated clockwiseand, in particular, to cover the top or upwardly open portion 57 of theU-shaped channel 56 to capture the rod 21, preferably without splayingof the arms 52 and 54. The base 128 has a lower or bottom surface 132with a centrally located pointed projection 133 for engaging andpenetrating the rod 21 at the rod surface 116. In certain embodimentsaccording to the invention, a circumferential rim (not shown) may alsoextend from the bottom surface 132, the rim providing additionalengagement points with the rod surface 116. The closure structure 18operably biases against the rod 21 by advancement and applies pressureto the rod 21 under torquing, so that the rod 21 is urged downwardlyagainst the shank top end surface 42 that extends into the channel 56.Downward biasing of the shank top surface 42 operably produces africtional engagement between the rod 21 and the surface 42 and alsourges the shank upper portion 8 toward the retaining structure 12 thathas been loaded into the receiver 10 and expanded into the groove 86, soas to frictionally engage the spherical surface 34 of the shank upperportion 8 with the spherical surface 95 of the retaining structure 12fixing the shank 4 in a selected, rigid position relative to thereceiver 10.

The closure structure break-off head 130 is secured to the base 128 at aneck 134 that is sized and shaped so as to break away at a preselectedtorque that is designed to properly seat the shank upper portion 8 inthe receiver 10. The break-off head 130 includes an external facetedsurface 135 that is sized and shaped to receive a conventional matingsocket type head of a driving tool (not shown) to rotate and torque theclosure structure 18. The break-off head 130 also includes a centralbore 137 and one or more grooves 138 for operably receiving manipulatingtools. Alternatively, a closure structure for use with the assembly 1may not include a break-off head, but rather simply have a cylindricalbody with a guide and advancement structure thereon and a top surfacewith an internal tool engagement structure formed therein, such as a hexaperture or a variety of internal tool-engaging forms of various shapes,such as a multi-lobular aperture sold under the trademark TORX, or thelike.

The illustrated closure structure 18 also includes an internal driveremoval tool engagement structure 140 in the form of an axially alignedaperture having a hex shape, disposed in the base 128. The internaldrive or aperture 140 is accessible after the break-off head 130 breaksaway from the base 128. The drive 140 is designed to receive a hex tool,of an Allen wrench type, for rotating the closure structure base 128subsequent to installation so as to provide for removal thereof, ifnecessary. Such a tool engagement structure may take a variety oftool-engaging forms and may include one or more apertures of variousshapes, such as a pair of spaced apart apertures, or a left handthreaded bore, or an easyout engageable step down bore, or amulti-lobular aperture, such as those sold under the trademark TORX, orthe like.

Prior to the polyaxial bone screw assembly 1 being placed in useaccording to the invention, the retaining structure 12 is preferablyfirst inserted about the bone screw shaft 6. This may be accomplished byeither placing the structure 12 over the tip 28 and moving the structure12 toward the upper portion 8 with the shaft 6 extending through thecentral channel 91 or inserting the structure 12 on the bone screw 4 atthe neck 26 of the shank body 6, with the end surfaces 100 and 101 beingpulled away from one another and pressed against and about the neck 26until the surfaces 100 and 101 expand around the neck 26 and then springback into a first position with the inner surface 95 facing the surface34 of the shank upper portion 8. The shank upper portion 8 and theconnected structure 12 are then simultaneously up or bottom-loaded intothe receiver through the opening 84 with the upper portion 8 beingplaced into the cavity 78. The structure 12 is manually compressed bypinching the surfaces 100 and 101 toward one another as the neck 26 isplaced into the opening 84 until the structure 12 is aligned with thegroove 86. The compressive force is then removed and the structure 12resiliently springs back and returns to the original ring-like orcollar-like orientation. Then, as illustrated in FIGS. 8 and 9, the topsurface 92, bottom surface 94 and outer cylindrical surface 104 of thestructure 12 frictionally engage the groove 86, fixing the retainingstructure 12 in the receiver 10 and capturing the shank upper portion 8within the receiver and in sliding, pivotal relationship with thespherical surface 95 of the retaining structure 12, and in certainangular orientations or articulations, with the spherical surface 82 ofthe receiver 10.

In an alternative method of installation, the bone screw shank upperportion 8 is first placed in the receiver 10 by inserting the upperportion 8 through the opening 84 and into the cavity 78. The retainingstructure 12 may then be placed over the shank body 6 at the tip 28 andmoved toward the shank upper portion 8. As with the previously describedinstallation method, the structure 12 is manually compressed by pinchingthe surfaces 100 and 101 toward one another as the structure 12 isplaced in the opening 84 until the structure 12 is aligned with thegroove 86. The compressive force is then removed and the structure 12resiliently springs back and returns to the original ring-like orcollar-like orientation, fixing the structure 12 in the receiver 10 andcapturing the shank upper portion 8 within the receiver cavity 78.

The capture structure 8 may then be manipulated into a positionsubstantially coaxial with the receiver 10 in readiness for boneimplantation. The assembly 1 is typically screwed into a bone, such asthe vertebra 15, by rotation of the shank 4 using a driving tool (notshown) that operably drives and rotates the shank 4 by engagementthereof with the faces 43 of the hexagonally shaped tool engagementstructure 41 of the shank 4. Preferably, when the driving tool engagesthe structure 41, a bottom or end portion thereof abuts the countersunkplanar seating surface 40 and outer surfaces of the driving tool engagethe walls that define the outer perimeter 44, providing an additionaldriving interface.

Typically, the receiver 10 and the retaining structure 12 are assembledon the shank 4 before inserting the shank body 6 into the vertebra 15 aspreviously described hereon. However, it is foreseen that in certaincircumstances, the shank body 6 can be first partially implanted withthe capture structure 8 extending proud to allow placement of theretaining structure 12 about the neck 26, followed by assembly with thereceiver 10. Then the shank body 6 can be further driven into thevertebra 15.

The vertebra 15 may be pre-drilled to minimize stressing the bone andhave a guide wire (not shown) inserted to provide a guide for theplacement and angle of the shank 4 with respect to the vertebra 15. Afurther tap hole may be made using a tap with the guide wire as a guide.Then, the assembly 1 or the solitary shank 4, is threaded onto the guidewire utilizing the cannulation bore 45 by first threading the wire intothe bottom opening 46 and then out of the top opening 48. The shank 4 isthen driven into the vertebra 15, using the wire as a placement guide.

With reference to FIGS. 8 and 9, the rod 21 is eventually positionedwithin the receiver U-shaped channel 56, and the closure structure ortop 18 is then inserted into and advanced between the arms 52 and 54 soas to bias or push against the rod 21. The break-off head 130 of theclosure structure 18 is twisted to a preselected torque, for example 90to 120 inch pounds, to urge the rod 21 downwardly. The shank top endsurface 42, because it is rounded to approximately equally extend upwardinto the channel 56 approximately the same amount no matter what degreeof rotation exists between the shank 4 and receiver 10 and because thesurface 42 is sized to extend upwardly into the U-shaped channel 56, thesurface 42 is engaged by the rod 21 and pushed downwardly toward thebase 50 of the receiver 10 when the closure structure 18 biasesdownwardly toward and onto the rod 21. The downward pressure on theshank 4 urges the shank top portion 8 downward toward the retainingstructure 12 and possibly against the receiver seating surface 82. Asthe closure structure 18 presses against the rod 21, the rod 21 pressesagainst the shank upper portion 8 that becomes frictionally, rigidlyattached to the receiver 10 at the retaining structure 12.

As previously described, FIG. 8 illustrates the polyaxial bone screwassembly 1 and including the rod 21 and the closure structure 18positioned at a level or extent of articulation in which the axis A ofthe bone screw shank and the axis B of the receiver are coaxial. FIGS. 9and 10 illustrate the assembly 1 with the axis A of the bone shank 4 atan angle with respect to the axis B of the receiver 10, and with theshank 4 being fixed in such angular locked configuration and implantedin the vertebra 15.

If removal of the assembly 1 and the associated rod 21 and the closurestructure 18 is necessary, disassembly is accomplished by using adriving tool (not shown) mating with driving surfaces of the aperture140 on the closure structure 18 to rotate the base 138 and reverse theadvancement thereof in the receiver 10. Then, disassembly of theassembly 1 is accomplished in reverse order to the procedure describedpreviously herein for assembly.

With reference to FIGS. 11-17, the reference numeral 201 generallyrepresents a second or alternative embodiment of a bone screw assemblyaccording to the present invention. The assembly 201 includes a shank204 that further includes a body 206 integral with an upwardly extendingupper portion or capture structure 208; a receiver 210; and anindependent open retaining structure 212. The shank 204, the receiver210 and the retaining structure 212 preferably are assembled prior toimplantation of the shank body 206 into a vertebra 215.

FIGS. 11 and 15-17 further show a closure structure 218 for compressingand biasing a longitudinal member such as a rod 221 against the shankupper portion 208 biasing the upper portion 208 into fixed frictionalcontact with the retaining structure 212 installed in the receiver 210,so as to fix the rod 221 relative to the vertebra 215. The receiver 210,the retaining structure 212 and the shank 204 cooperate in such a mannerthat the receiver 210 and the shank 204 can be secured at any of aplurality of angles, articulations or rotational alignments relative toone another and within a selected range of angles both from side to sideand from front to rear, to enable flexible or articulated engagement ofthe receiver 210 with the shank 204 until both are locked or fixedrelative to each other near an end of an implantation procedure.

The shank 204, best illustrated in FIGS. 11-14, is elongate, with theshank body 206 having a helically wound bone implantable thread 224extending from near a neck 226 located adjacent to the shank upperportion 208 to a tip 228 of the body 206 and extending radiallyoutwardly therefrom. During use, the body 206 utilizing the thread 224for gripping and advancement is implanted into the vertebra 215 leadingwith the tip 228 and driven down into the vertebra 215 with aninstallation or driving tool (not shown), so as to be implanted in thevertebra 215 to near the neck 226, as shown in FIG. 17, and as isdescribed more fully in the paragraphs below. The shank 204 has anelongate axis of rotation generally identified by the reference letterD.

The neck 226 extends axially outwardly and upwardly from the shank body206. With particular reference to FIG. 12-13, the illustrated neck 226is of reduced radius as compared to the shank body 206 and an outerdiameter of the thread 224. Further extending axially and outwardly fromthe neck 226 is the shank upper portion 208 that provides a connectiveor capture structure disposed at a distance from the thread 224 and thusat a distance from the vertebra 215 when the body 206 is implanted inthe vertebra 215.

The shank upper portion 208 is configured for connecting the shank 204to the receiver 210 and capturing the shank 204 in the receiver 210.With particular reference to FIGS. 12-14, the upper portion 208 has anouter, convex and substantially spherical surface 234 that extendsoutwardly and upwardly from the neck 226 and terminates at asubstantially planar top surface 238. The spherical surface 234 has anouter radius configured for sliding cooperation and ultimate frictionalmating with a concave surface of the retaining structure 212 and asubstantially spherical inner surface of the receiver 210, having asubstantially similar radius, discussed more fully in the paragraphsbelow. The flat surface 238 is substantially perpendicular to the axisD. The spherical surface 234 shown in the present embodiment is smooth,but it is foreseen that the surface 234 may include a roughened ortextured surface or surface finish, or may be scored, knurled, or thelike, for enhancing frictional engagement with the retaining structure212 and the receiver 210. A counter sunk substantially planar base orseating surface 240 partially defines an internal drive feature orimprint 241. The illustrated internal drive feature 241 is an apertureformed in the top 238 and has a hex shape designed to receive a hex toolof an Allen wrench type, into the aperture for rotating and driving thebone screw shank 204. It is foreseen that such an internal toolengagement structure may take a variety of tool-engaging forms and mayinclude one or more apertures of various shapes, such as a pair ofspaced apart apertures or a multi-lobular aperture, such as those soldunder the trademark TORX, or the like. The seat or base 240 of the drivefeature 241 is disposed perpendicular to the axis D with the drivefeature 241 otherwise being coaxial with the axis D. Six driving facesor walls 242, each disposed parallel to the axis D also define thefeature 241. The planar top surface 238 extends from a hexagonal outerperimeter 244 defined by the driving faces 242 and terminates at acircular edge 243. The circular edge 243 also defines a top orterminating upper edge of the spherical outer surface 234. In operation,a driving tool (not shown) is received in the internal drive feature241, being seated at the base 240 and engaging the faces 242 for bothdriving and rotating the shank body 206 into the vertebra 215.

The shank 204 shown in the drawings is cannulated, having a smallcentral bore 245 extending an entire length of the shank 204 along theaxis D, coaxial with the threaded body 206. The bore 245 has a firstcircular opening 246 at the shank tip 228 and a second circular opening248 at the driving feature seating surface 240. The bore 245 provides apassage through the shank 204 interior for a length of wire (not shown)inserted into the vertebra 215 prior to the insertion of the shank body206, the wire providing a guide for insertion of the shank body 206 intothe vertebra 215.

Referring to FIGS. 11 and 15-16, the receiver 210 has an axis ofrotation E and is substantially similar to the receiver 10 previouslydescribed herein. Thus, the description of the receiver 10 isincorporated by reference with respect to the receiver 210.Specifically, the receiver 210 includes a receiver base 250, arms 252and 254, a U-shaped channel 256 with an upper opening 257, a lower seat258, an interior surface 260, guide and advancement structure 262, gripbores 264, recesses 266, a chamber or cavity 278, a lower inner surface280, an inner spherical surface 282, a ridge 283, a lower opening 284, abase exterior 285 and a groove 286 the same or substantially similar tothe respective base 50, arms 52 and 54, U-shaped channel 56 with upperopening 57, lower seat 58, interior surface 60, guide and advancementstructure 62, grip bores 64, recesses 66, cavity 78, lower inner surface80, inner spherical surface 82, ridge 83, lower opening 84, baseexterior 85 and groove 86 previously described herein with respect tothe receiver 10 of the assembly 1. As discussed earlier with respect tothe assembly 1, as compared to the receiver 10, the receiver 210 lowersurface 280 is substantially cylindrical while the lower surface 80 ismostly spherical.

The retaining structure or collar 212 that is used to retain the capturestructure 208 of the shank 204 within the receiver 210 is bestillustrated in FIGS. 11 and 15-16. The structure 212 has a central axisF that is operationally the same as the axis E associated with thereceiver 210 when the capture structure 208 and the retaining structure212 are installed within the receiver 210. The retaining structure 212is the same or substantially similar to the retaining structure 12previously described herein and thus the description of the structure 12is incorporated by reference herein with respect to the structure 212.Specifically, the structure 212 includes a central channel 291, a top292, a bottom 294, a partially spherical inner surface 295, a conicalsurface or chamfer 298, end surfaces 300 and 301 and an outercylindrical surface 304, the same or substantially similar to respectivecentral channel 91, top 92, bottom 94, spherical inner surface 95,conical surface 98, end surfaces 100 and 101 and outer cylindricalsurface 104 of the retaining structure 12.

A width or space between the surfaces 300 and 301 is determined by adesired amount of compressibility of the open retaining structure 212when loaded into the receiver 210. The space shown in FIG. 11 betweenthe surfaces 300 and 301 provides an adequate distance between thesurfaces 300 and 301 for the retaining structure 212 to be pinched, withthe surfaces 300 and 301 compressed toward one another to an almosttouching or touching configuration, to an extent that the compressedretaining structure 212 is up or bottom loadable through the opening284. As illustrated in FIG. 11, the surfaces 300 and 301 aresubstantially parallel and vertical, however, it is foreseen that it maybe desirable to orient the surfaces obliquely or at a slight angledepending upon the amount of compression desired during loading of theretaining and articulating structure 212 into the receiver 210. Afterpassing through the opening 284 and along a portion of the cylindricalinner surface 280, the retaining structure 212 expands or springs backto an original uncompressed, rounded or collar-like configuration oncein the groove 286. FIGS. 15 and 16 illustrate the structure 212 in afully installed position in the receiver 210 and having an articulatingor swiveling relationship with the upper portion 208 of the bone screwshank 204 wherein the bone screw upper portion 208 is slidable withrespect to the retaining structure 212 at the surface 295.

The elongate rod or longitudinal member 221 that is utilized with theassembly 201 can be any of a variety of implants utilized inreconstructive spinal surgery, but is normally a cylindrical elongatestructure having a smooth cylindrical surface 316 of uniform diameter.The rod 221 is preferably sized and shaped to snugly seat near thebottom of the U-shaped channel 256 of the receiver 210 and, duringnormal operation, is positioned slightly above the bottom of the channel256 at the lower seat 258. In particular, the rod 221 directly orabutingly engages the upper portion 208 of the shank 204 either at thetop 238, the circular edge 243 or the spherical surface 234, as shown inFIGS. 15 and 16, and is biased against the upper portion 208,consequently biasing the shank 204 downwardly in a direction toward thebase 250 of the receiver 210 when the assembly 201 is fully assembled.For this to occur, the shank upper portion 208 must extend at leastslightly into the space of the channel 256 when engaging the retainingstructure 212. The shank 204 is thereby locked or held in positionrelative to the receiver 210 by the rod 221 firmly pushing downward onthe shank upper portion 208.

With reference to FIGS. 11 and 15-17, the closure structure or closuretop 218 can be any of a variety of different types of closure structuresfor use in conjunction with the present invention with suitable matingstructure on the upstanding arms 252 and 254. In the embodiment shown,the closure top 218 is rotatably received between the spaced arms 252and 254. It is foreseen that a mating and advancement structure could belocated on the external surfaces of the arms 252 and 254 for mating witha closure top.

The illustrated closure structure 218 is substantially cylindrical,having a top 328 and a bottom 329. The closure structure 218 furtherincludes a helically wound guide and advancement structure 331 that issized, shaped and positioned so as to engage the guide and advancementstructure 262 on the arms 252 and 254 to provide for rotatingadvancement of the closure structure 218 into the receiver 210 whenrotated clockwise and, in particular, to cover the top or upwardly openportion 257 of the U-shaped channel 256 to capture the rod 221,preferably without splaying of the arms 252 and 254. The closurestructure bottom 329 includes a centrally located pointed projection 333for engaging and penetrating the rod 221 at the rod surface 316. Incertain embodiments according to the invention, a circumferential rim(not shown) may also extend from the bottom surface 329, the rimproviding additional engagement points with the rod surface 316. Theclosure structure 218 operably biases against the rod 221 by advancementand applies pressure to the rod 221, so that the rod 221 is urgeddownwardly against the shank upper portion 208 that extends into thechannel 256. Downward biasing of the shank upper portion 208 operablyproduces a frictional engagement between the rod 221 and the upperportion 208 and also urges the shank upper portion 208 toward theretaining structure 212 that has been loaded into the receiver 210 andexpanded into the groove 286, so as to frictionally engage the sphericalsurface 234 of the shank upper portion 208 with the spherical surface295 of the retaining structure 212 fixing the shank 204 in a selected,rigid position relative to the receiver 210. It is noted that becausethe illustrated shank upper portion 208 includes the flat surface 238,circular edge 243 and spherical surface 234 and the rod 221 may engageany of such surfaces, the rod 221 may be seated at a distance from thereceiver lower seat 258 and the closure structure 218 may not bedisposed flush to a top of the receiver 210 when fully engaged with therod 221 biasing the rod 221 into locking engagement with the shank 204.Such placement of the closure structure 218 and the rod 221 does nothinder the closure structure 218 from seating in the receiver 210 andfixing the rod 221 in a locked position within the receiver 210.

Formed in the closure structure 218 top surface 328 is an internal drivefeature 336 sized and shaped to receive a mating driving tool (notshown) to rotate and torque the closure structure 218 against the rod221. The illustrated drive feature 336 is multi-lobular, but it isforeseen that the internal drive feature may be a hex aperture or avariety of internal tool-engaging forms of various shapes. The drivefeature 336 may also be used to remove the closure structure 218 fromthe receiver 210 subsequent to installation, if desired or necessary.

Prior to the polyaxial bone screw assembly 201 being placed in useaccording to the invention, the retaining structure 212 is preferablyfirst inserted about the bone screw shaft 206. This may be accomplishedby either placing the structure 212 over the tip 228 and moving thestructure 212 toward the upper portion 208 with the shaft 206 extendingthrough the central channel 291 or inserting the structure 212 on thebone screw 204 at the neck 226 of the shank body 206, with the endsurfaces 300 and 301 being pulled away from one another and pressedagainst and about the neck 226 until the surfaces 300 and 301 expandaround the neck 226 and then spring back into a first position with theinner surface 295 facing the surface 234 of the shank upper portion 208.The shank upper portion 208 and the connected structure 212 are thensimultaneously up or bottom-loaded into the receiver through the opening284 with the upper portion 208 being placed into the cavity 278. Thestructure 212 is manually compressed by pinching the surfaces 300 and301 toward one another as the neck 226 is placed into the opening 284until the structure 212 is aligned with the groove 286. The compressiveforce is then removed and the structure 212 resiliently springs back andreturns to the original ring-like or collar-like orientation. Then, asillustrated in FIG. 15, the top surface 292, bottom surface 294 andouter cylindrical surface 304 of the structure 212 frictionally engagethe groove 286, fixing the retaining structure 212 in the receiver 210and capturing the shank upper portion 208 within the receiver and insliding, pivotal relationship with the spherical surface 295 of theretaining structure 212 and with the spherical surface 282 of thereceiver 210.

In an alternative method of installation, the bone screw shank upperportion 208 is first placed in the receiver 210 by inserting the upperportion 208 through the opening 284 and into the cavity 278. Theretaining structure 212 may then be placed over the shank body 206 atthe tip 228 and moved toward the shank upper portion 208. As with thepreviously described installation method, the structure 212 is manuallycompressed by pinching the surfaces 300 and 301 toward one another asthe structure 212 is placed in the opening 284 until the structure 212is aligned with the groove 286. The compressive force is then removedand the structure 212 resiliently springs back and returns to theoriginal ring-like or collar-like orientation, fixing the structure 212in the receiver 210 and capturing the shank upper portion 208 within thereceiver cavity 278.

The capture structure 208 may then be manipulated into a positionsubstantially coaxial with the receiver 210 in readiness for boneimplantation. The assembly 201 is typically screwed into a bone, such asthe vertebra 215, by rotation of the shank 204 using a driving tool (notshown) that operably drives and rotates the shank 204 by engagementthereof with the base 240 and the faces 242 of the internal drivefeature 241.

Typically, the receiver 210 and the retaining structure 212 areassembled on the shank 204 before inserting the shank body 206 into thevertebra 215 as previously described hereon. However, it is foreseenthat in certain circumstances, the shank body 206 can be first partiallyimplanted with the capture structure 208 extending proud to allowplacement of the retaining structure 212 about the neck 226, followed byassembly with the receiver 210. Then the shank body 206 can be furtherdriven into the vertebra 215.

The vertebra 215 may be pre-drilled to minimize stressing the bone andhave a guide wire (not shown) inserted to provide a guide for theplacement and angle of the shank 204 with respect to the vertebra 215. Afurther tap hole may be made using a tap with the guide wire as a guide.Then, the assembly 201 or the solitary shank 204, is threaded onto theguide wire utilizing the cannulation bore 245 by first threading thewire into the bottom opening 246, then out of the top opening 248 andthen through and out of the driving feature 241. The shank 204 is thendriven into the vertebra 215, using the wire as a placement guide.

With reference to FIGS. 15-17, the rod 221 is eventually positionedwithin the receiver U-shaped channel 256, and the closure structure ortop 218 is then inserted into and advanced between the arms 252 and 254so as to bias or push against the rod 221 and urge the rod 221downwardly. Depending on a desired amount of articulation between theshank body 206 and the receiver 210, the rod 221 comes into contactedwith the planar top surface 238 (shown in FIG. 15), the circular edge243 (shown in FIG. 16) or the spherical surface 234 of the shank upperportion 208 and such surface is engaged by the rod 221 and pusheddownwardly toward the base 250 of the receiver 210 when the closurestructure 218 biases downwardly toward and onto the rod 221. Thedownward pressure on the shank 204 urges the shank top portion 208downward toward the retaining structure 212 and typically against thereceiver seating surface 282. As the closure structure 218 pressesagainst the rod 221, the rod 221 presses against the shank upper portion208 that becomes frictionally, rigidly attached to the receiver 210 atthe retaining structure 212.

FIGS. 15-17 illustrates the polyaxial bone screw assembly 201 andincluding the rod 221 and the closure structure 218 positioned atvarious articulations or locked angular orientations in which the axis Dof the bone screw shank and the axis E of the receiver are not coaxial.FIG. 17 also shows the shank 204 implanted in the vertebra 15. Aspreviously described, full locking installation is obtainable when therod 221 engages the rim 243 or the spherical surface 234, even thoughsuch engagement places the rod 221 higher in the channel 256 andtherefore the closure structure 218 does not seat in a manner that isflush with the top surface of the receiver 210.

If removal of the assembly 201 and the associated rod 221 and theclosure structure 218 is necessary, disassembly is accomplished by usinga driving tool (not shown) mating with the internal drive 336 on theclosure structure 218 to rotate the structure 218 and reverse theadvancement thereof in the receiver 210. Then, disassembly of theassembly 201 is accomplished in reverse order to the procedure describedpreviously herein for assembly.

With reference to FIGS. 18-27, the reference numeral 401 generallyrepresents a third or alternative embodiment of a bone screw assemblyaccording to the present invention. The assembly 401 includes a shank404 that further includes a body 406 integral with an upwardly extendingupper portion or capture structure 408; a receiver 410; and anindependent open retaining structure 412. The shank 404, the receiver410 and the retaining structure 412 preferably are assembled prior toimplantation of the shank body 406 into a vertebra 415.

FIGS. 18 and 25-27 further show a closure structure 418 for compressingand biasing a longitudinal member such as a rod 421 against the shankupper portion 408 biasing the upper portion 408 into fixed frictionalcontact with the retaining structure 412 installed in the receiver 410,so as to fix the rod 421 relative to the vertebra 415. The receiver 410,the retaining structure 412 and the shank 404 cooperate in such a mannerthat the receiver 410 and the shank 404 can be secured at any of aplurality of angles, articulations or rotational alignments relative toone another and within a selected range of angles both from side to sideand from front to rear, to enable flexible or articulated engagement ofthe receiver 410 with the shank 404 until both are locked or fixedrelative to each other near an end of an implantation procedure.

The shank 404, best illustrated in FIGS. 18 and 22-24, is elongate, withthe shank body 406 having a helically wound bone implantable thread 424extending from near a neck 426 located adjacent to the shank upperportion 408 to a tip 428 of the body 406 and extending radiallyoutwardly therefrom. During use, the body 406 utilizing the thread 424for gripping and advancement is implanted into the vertebra 415 leadingwith the tip 428 and driven down into the vertebra 415 with aninstallation or driving tool (not shown), so as to be implanted in thevertebra 415 to near the neck 426, as shown in FIG. 27, and similar towhat has been described previously with respect to the similar bonescrew assemblies 1 and 201. The shank 404 has an elongate axis ofrotation generally identified by the reference letter G.

The neck 426 extends axially outwardly and upwardly from the shank body406. With particular reference to FIGS. 22-23, the illustrated neck 426is of reduced radius as compared to the shank body 406 and an outerdiameter of the thread 424. Further extending axially and outwardly fromthe neck 426 is the shank upper portion 408 that provides a connectiveor capture structure disposed at a distance from the thread 424 and thusat a distance from the vertebra 415 when the body 406 is implanted inthe vertebra 415.

The shank upper portion 408 is configured for connecting the shank 404to the receiver 410 and capturing the shank 404 in the receiver 410. Theupper portion 408 has an outer, lower, convex and partially sphericalsurface 434 that extends outwardly and upwardly from the neck 426 andterminates at a substantially planar annular surface 436. A second,upper convex partially spherical surface 437 extends from the planarsurface 436 to a planar and annular top surface 438.

The lower spherical surface 434 is substantially hemispherical and hasan outer radius configured for sliding cooperation and ultimatefrictional mating with a concave surface of the retaining structure 412and a substantially spherical inner surface of the receiver 410, havinga substantially similar radius, discussed more fully below. The planaror flat surfaces 436 and 438 are both substantially perpendicular to theshank axis G. The partially spherical surface 434 shown in the presentembodiment is smooth, but it is foreseen that the surface 434 mayinclude a roughened or textured surface or surface finish, or may bescored, knurled, or the like, for enhancing frictional engagement withthe retaining structure 412 and the receiver 410.

The upper, partially spherical surface 437 has a radius that is smallerthan the radius of the lower spherical surface 434. A compared to theassembly 201 that has the shank 204 with the substantially sphericalsurface 234, the pair of spherical surfaces 434 and 437 of the shankupper portion 408 cooperate with the smaller upper spherical surface 437providing a more compact structure with greater clearance between theupper spherical surface 437 and the inner walls of the receiver 410 thanavailable to the single spherical surface 234, allowing for ease inarticulation and a slightly greater degree of angulation of the shank408 with respect to the receiver 410 than provided by the assembly 201.

A counter sunk substantially planar base or seating surface 440partially defines an internal drive feature or imprint 441. Theillustrated internal drive feature 441 is an aperture formed in the top438 and has a hex shape designed to receive a hex tool of an Allenwrench type, into the aperture for rotating and driving the bone screwshank 404. It is foreseen that such an internal tool engagementstructure may take a variety of tool-engaging forms and may include oneor more apertures of various shapes, such as a pair of spaced apartapertures or a multi-lobular aperture, such as those sold under thetrademark TORX, or the like. The seat or base 440 of the drive feature441 is disposed perpendicular to the axis G with the drive feature 441otherwise being coaxial with the axis G. Six driving faces or walls 442,each disposed parallel to the axis G also define the feature 441. Theplanar top surface 438 extends from a hexagonal outer perimeter 444defined by the driving faces 442 and terminates at a circular edge 443.The circular edge 443 also defines a top or terminating upper edge ofthe upper spherical outer surface 437. In operation, a driving tool (notshown) is received in the internal drive feature 441, being seated atthe base 440 and engaging the faces 442 for both driving and rotatingthe shank body 406 into the vertebra 415.

The shank 404 shown in the drawings is cannulated, having a smallcentral bore 445 extending an entire length of the shank 404 along theaxis G, coaxial with the threaded body 406. The bore 445 has a firstcircular opening 446 at the shank tip 428 and a second circular opening448 at the driving feature seating surface 440. The bore 445 provides apassage through the shank 404 interior for a length of wire (not shown)inserted into the vertebra 415 prior to the insertion of the shank body406, the wire providing a guide for insertion of the shank body 406 intothe vertebra 415.

Referring to FIGS. 21 and 25-26, the receiver 410 is substantiallysimilar to the receivers 10 and 210 previously described herein and thusthose descriptions are incorporated by reference herein with respect tothe receiver 410. The receiver 410 has an axis of rotation H and furtherincludes a receiver base 450, arms 452 and 454, a U-shaped channel 456with an upper opening 457, a lower seat 458, an interior surface 460,guide and advancement structure 462, grip bores 464, a chamber or cavity478, a lower inner surface 480, an upper inner spherical surface 482, aridge 483, a lower opening 484, a base exterior 485 and a groove 486 thesame or substantially similar to the respective base 50, arms 52 and 54,U-shaped channel 56 with upper opening 57, lower seat 58, interiorsurface 60, guide and advancement structure 62, grip bores 64, cavity78, lower inner surface 80, upper inner spherical surface 82, ridge 83,lower opening 84, base exterior 85 and groove 86 previously describedherein with respect to the receiver 10 of the assembly 1.

Although not shown, the grip bores 464 may include recesses similar tothe recesses 66 described herein with respect to the assembly 1. Also atthe opening 484, the surface is substantially cylindrical, having aradius sufficient to allow for the uploading of the shank upper portion408 through the opening 484 and beyond the groove 486 and into thechamber 478 in slidable engagement with the surfaces 480 and 482, withthe ridge 483 providing a stop so that the upper portion 408 isprohibited from passing through the U-shaped channel 456. As with thepreviously described embodiments, the lower inner surface 480 disposedabove and adjacent the groove 486 may be a continuation of the sphericalsurface 482 as shown in FIG. 21 or in some embodiments, the lower innersurface 480 may be substantially cylindrical in form as illustrated inFIGS. 15 and 16 with respect to the assembly 201.

The receiver 410 also differs slightly from the previously describedreceivers 10 and 210 in outward configuration or form. For example, thebase 450 is substantially cylindrical in outer form and the arms 452 and454 include added outwardly extending material or thickness, providingthe same basic functions as the bases and arms of the receivers 10 and210, but advantageously reducing bulk where not necessary at the base,and adding bulk, and thus strength, at the arms 452 and 454.

The retaining structure or collar 412 that is used to retain the capturestructure 408 of the shank 404 within the receiver 410 is bestillustrated in FIGS. 18-20. The structure 412 has a central axis I thatis operationally the same as the axis H associated with the receiver 410when the capture structure 408 and the retaining structure 412 areinstalled within the receiver 410. The retaining structure 412 is thesame or substantially similar to the retaining structure 12 previouslydescribed herein and thus the description of the structure 12 isincorporated by reference herein with respect to the structure 412.Specifically, the structure 412 includes a central channel 491, a top492, a bottom 494, a substantially spherical inner surface 495, endsurfaces 500 and 501 and an outer cylindrical surface 504, the same orsubstantially similar to respective central channel 91, top 92, bottom94, spherical inner surface 95, end surfaces 100 and 101 and outercylindrical surface 104 of the retaining structure 12. Unlike thestructure 12, the structure 412 does not include a lower inner chamfer.The entire inner surface of the structure 412 is substantiallyspherical. However, it is foreseen that the structure 412 may includesuch a sloping or conical chamfer or bevel.

Similar to what has been previously described herein with respect to thewidth X of the structure 12 and the width between surfaces 300 and 301of the structure 212, a width or space between the surfaces 500 and 501is determined by a desired amount of compressibility of the openretaining structure 512 when loaded into the receiver 510. The space ordistance between the surfaces 500 and 501 shown in FIG. 19 providesadequate space between the surfaces 500 and 501 for the retainingstructure 412 to be pinched, with the surfaces 500 and 501 compressedtoward one another to an almost touching or touching configuration, toan extent that the compressed retaining structure 412 is up or bottomloadable through the opening 484. After passing through the opening 484and along a portion of the cylindrical inner surface, the retainingstructure 412 expands or springs back to an original uncompressed,rounded or collar-like configuration once in the groove 486. FIGS. 25and 26 illustrate the structure 412 in a fully installed position in thereceiver 410 and having an articulating or swiveling relationship withthe lower spherical portion 434 of the bone screw shank 404.

The elongate rod or longitudinal member 421 that is utilized with theassembly 401 can be any of a variety of implants utilized inreconstructive spinal surgery, but is normally a cylindrical elongatestructure having a smooth cylindrical surface 516 of uniform diameter.The rod 421 is the same or substantially similar to the rods 21 and 221previously described herein. With reference to FIGS. 25 and 26, the rod421 directly or abutingly engages the upper portion 408 of the shank 404either at the top 438, the circular edge 443 or the upper sphericalsurface 437, and is biased against the upper portion 408, consequentlybiasing the shank 404 downwardly in a direction toward the base 450 ofthe receiver 410 when the assembly 401 is fully assembled. For this tooccur, the shank upper portion 408 must extend at least slightly intothe space of the channel 456 when engaging the retaining structure 412.The shank 404 is thereby locked or held in position relative to thereceiver 410 by the rod 421 firmly pushing downward on the shank upperportion 408.

With reference to FIGS. 18 and 25-27, the closure structure or closuretop 418 can be any of a variety of different types of closure structuresfor use in conjunction with the present invention with suitable matingstructure on the upstanding arms 452 and 454. In the embodiment shown,the closure top 418 is rotatably received between the spaced arms 452and 454. It is foreseen that a mating and advancement structure could belocated on the external surfaces of the arms 452 and 454 for mating witha closure top.

The illustrated closure structure 418 is substantially similar to thebreak-off closure structure 18 previously described herein. Thestructure 418 includes a base 528, a break-off head 530, a guide andadvancement structure 531, a bottom surface 532 having a projection orpoint 533, a neck 534, and external faceted surface 535, a central bore537 and an internal drive 540 in the base 528 substantially similar tothe respective base 128, break-off head 130, guide and advancementstructure 131, bottom surface 132, point 133, neck 134, external facetedsurface 135, central bore 137 and internal drive 140 in the base 128 ofthe closure structure 18. When installed, the closure structure 418operably biases against the rod 421 by advancement and applies pressureto the rod 421, so that the rod 421 is urged downwardly against theshank upper portion 408 that extends into the channel 456. Downwardbiasing of the shank upper portion 408 operably produces a frictionalengagement between the rod 421 and the shank upper portion 408 and alsourges the shank upper portion 408 toward the retaining structure 412that has been loaded into the receiver 410 and expanded into the groove486, so as to frictionally engage the lower spherical surface 434 of theshank upper portion 408 with the spherical surface 495 of the retainingstructure 412 fixing the shank 404 in a selected, rigid positionrelative to the receiver 410. Similar to the assembly 201 previouslydescribed herein, it is noted that because the illustrated shank upperportion 408 includes the flat surface 438, circular edge 443 andspherical surface 437 and the rod 421 may engage any of such surfaces,the rod 421 may be seated at a distance from the receiver lower seat 458and the closure structure base 528 may not be disposed flush to a top ofthe receiver 410 when the break-off head 530 has been broken off and thebase 528 is fully engaged with the rod 421 biasing the rod 421 intolocking engagement with the shank 404. Such placement of the closurestructure 418 and the rod 421 does not hinder the closure structure 418from seating in the receiver 410 and fixing the rod 421 in a lockedposition within the receiver 410.

In use, the assembly 401 is assembled, implanted, utilized, disassembledand removed identically or substantially similarly to what has beenpreviously described herein with respect to the assembly 1. Thereforesuch discussion is incorporated by reference herein with respect to theassembly 401.

FIGS. 25 and 26 illustrate the polyaxial bone screw assembly 401 andincluding the rod 421 and the closure structure 418 positioned atvarious articulations or locked angular orientations: one in which theaxis G of the bone screw shank is coaxial with the axis H of thereceiver (FIG. 25); and one in which the axis G of the bone screw shankand the axis H of the receiver are not coaxial (FIG. 26). FIG. 27 alsoshows the shank 404 implanted in the vertebra 415. As previouslydescribed, full locking installation is obtainable when the rod 421engages the top surface 438, the rim 443 or the upper spherical surface437, even though such engagement places the rod 421 higher in thechannel 456 and therefore the closure structure 418 does not seat in amanner that is flush with the top surface of the receiver 410.

With reference to FIGS. 28-33, the reference numeral 601 generallyrepresents a fourth embodiment of a bone screw assembly according to thepresent invention. The assembly 601 includes a shank 604 having an axisof rotation J that further includes a body 606 integral with an upwardlyextending upper portion or capture structure 608; a receiver 610 havingan axis of rotation K; and an independent open retaining structure 612having an axis of rotation L. The shank 604, the receiver 610 and theretaining structure 612 preferably are assembled prior to implantationof the shank body 606 into a vertebra. FIGS. 28, 32 and 33 further showa closure structure 618 for compressing and biasing a longitudinalmember such as a rod 621 against the shank upper portion 608 biasing theupper portion 608 into fixed frictional contact with the retainingstructure 612 installed in the receiver 610, so as to fix the rod 621relative to the vertebra 615. The receiver 610, the retaining structure612 and the shank 604 cooperate in such a manner that the receiver 610and the shank 604 can be secured at any of a plurality of angles,articulations or rotational alignments relative to one another andwithin a selected range of angles both from side to side and from frontto rear, to enable flexible or articulated engagement of the receiver610 with the shank 604 until both are locked or fixed relative to eachother near an end of an implantation procedure.

The shank 604, best illustrated in FIGS. 29-31, is elongate, with theshank body 606 and the upper portion 608 being substantially similar tothe shank body 6 and upper portion 8 of the shank 4 previously describedherein. Furthermore, the shank 605 includes a thread 624, a neck 626, atip 628, an upper portion partially spherical surface 634, seatingsurface 640, a tool engagement structure 641, a top 642 and acannulation bore 645 identical or substantially similar to the thread24, neck 26, tip 28, upper portion spherical surface 34, seating surface40, tool engagement structure 41, top 42 and cannulation bore 45 of theshank 4. Therefore a description of these features will not be repeatedhere with the exception of the seating surface 640. The shank upperportion 608 does not include an annular surface 38 cooperating with therecessed seating surface 40 described herein with respect to the shankupper portion 8. Rather, the seating surface 640 of the shank upperportion 608 extends or slopes outwardly and upwardly from the toolengagement structure 641 to the substantially spherical surface 634 asbest illustrated in FIG. 30. It is noted that in smaller embodiments ofbone screws according to the invention, it may be difficult to machineor otherwise form the recessed surface 38 into the bone screw upperportion 8 (illustrated in FIGS. 6 and 7). In such embodiments, the moreeasily formable sloping seating surface 640 provides adequate seatingsurface about the tool engagement structure 641 and a slightly elongatedtool engagement structure 641 for rotating and implantation of the bonescrew shank body 606 into a vertebra.

Referring to FIGS. 28, 32 and 33, the receiver 610 is substantiallysimilar to the receiver 410 previously described herein with oneexception, the type of helically wound guide and advancement structurefor use in cooperation with the closure structure 618. Specifically, thereceiver 610 includes a receiver base 650, arms 652 and 654, a U-shapedchannel 656 with an upper opening 657, a lower seat 658, and an interiorsurface 660 identical or substantially similar to the receiver base 450,arms 452 and 454, U-shaped channel 456 with an upper opening 457, lowerseat 458, and the interior surface 460 of the receiver 410. The receiver610 includes a guide and advancement structure 662 that is locatedwithin the receiver 610 similarly to the guide and advancement structure462 of the receiver 410. However, the guide and advancement structure462 is a flange form while the guide and advancement structure 662 is areverse angle form, best illustrated in FIGS. 32 and 33. The receiver610 further includes grip bores 664, an inner chamber or cavity 678having a spherical surface and a groove 686 that is identical orsubstantially similar to the respective grip bores 464, and innerchamber 678 features, including the groove 486 of the receiver 410 ofthe assembly 401.

The retaining structure or collar 612 that is used to retain the capturestructure 608 of the shank 604 within the receiver 610 is bestillustrated in FIGS. 28 and 32-33. The structure 612 is identical orsubstantially similar to the retaining structure 412 previouslydescribed herein.

The elongate rod or longitudinal member 621 that is utilized with theassembly 601 can be any of a variety of implants utilized inreconstructive spinal surgery, but is normally a cylindrical elongatestructure having a smooth cylindrical surface 687 of uniform diameter.The rod 621 is substantially similar in form and function to the rods21, 221 and 421 previously described herein.

With reference to FIGS. 28 and 32-33, the closure structure or closuretop 618 can be any of a variety of different types of closure structuresfor use in conjunction with the present invention with suitable matingstructure on the upstanding arms 652 and 654. In the embodiment shown,the closure top 618 is rotatably received between the spaced arms 652and 654. It is foreseen that a mating and advancement structure could belocated on the external surfaces of the arms 652 and 654 for mating witha closure top.

The illustrated closure structure 618 is substantially similar to thebreak-off closure structure 418 previously described herein with theexception that the structure 618 has a reverse angle helical form guideand advancement structure 691, rather than the flange form guide andadvancement structure 531 of the closure structure 418.

Specifically, the structure 618 includes a base 688, a break-off head690, a bottom surface 692 having a projection or point 693, a neck 694,and external faceted surface 695, a central bore 697 and an internaldrive 698 in the base 688 substantially similar to the respective base528, break-off head 530, bottom surface 532, point 533, neck 534,external faceted surface 535, central bore 537 and internal drive 540 inthe base 528 of the closure structure 418.

When installed, the closure structure 618 operably biases against therod 621 by advancement and applies pressure to the rod 621, so that therod 621 is urged downwardly against the shank upper portion 608 thatextends into the channel 656. Downward biasing of the shank upperportion 608 operably produces a frictional engagement between the rod621 and the shank upper portion 608 and also urges the shank upperportion 608 toward the retaining structure 612 that has been loaded intothe receiver 610 and expanded into the groove 686, so as to frictionallyengage the spherical surface 634 of the shank upper portion 608 with theinner spherical surface of the retaining structure 612 fixing the shank604 in a selected, rigid position relative to the receiver 610.

In use, the assembly 601 is assembled, implanted, utilized, disassembledand removed identically or substantially similarly to what has beenpreviously described herein with respect to the assembly 1. Thereforesuch discussion is incorporated by reference herein with respect to theassembly 601.

FIGS. 32 and 33 illustrate the polyaxial bone screw assembly 601 andincluding the rod 621 and the closure structure 618 positioned atvarious articulations or locked angular orientations: one in which theaxis J of the bone screw shank is coaxial with the axis K of thereceiver (FIG. 32); and one in which the axis J of the bone screw shankand the axis K of the receiver are not coaxial (FIG. 33).

It is to be understood that while certain forms of the present inventionhave been illustrated and described herein, it is not to be limited tothe specific forms or arrangement of parts described and shown.

1. A polyaxial bone screw assembly comprising: a) a bone screw shankhaving an upper portion with a capture structure having a lower convexpartially spherically shaped first surface; b) a receiver having a pairof arms forming a channel, the receiver also having a cavity with aconcave partially spherically shaped second surface adapted to receiveand allow pivotal movement of the shank first surface during positioningand an opening to an exterior of the receiver opposite the pair of arms,the cavity communicating with the channel, the bone screw upper portionbeing uploaded and received in the cavity through the opening; thereceiver having a lower groove within the cavity; c) a retainingstructure being receivable in the cavity and securable to the receiverin fixed relation thereto when the shank upper portion is in thereceiver, the retaining structure being outwardly biased and received inthe receiver lower groove; the retaining structure having a thirdsurface sized and shaped to receive a portion of the shank firstsurface, the retaining structure being sized and shaped to retain theshank upper portion within the receiver cavity, the shank upper portionsized and shaped to extend above the retaining structure and receivedirect downward force from direct forceful engaging contact between therod and the shank when the shank upper portion is retained in the cavityby the retaining structure such that all downward force from the rod isapplied directly to the shank and so as to lock the angular position ofthe receiver relative to the shank in a locked position due to thedirect forceful contact between the rod and the shank, the assemblyhaving an unlocked position wherein the shank upper portion is insliding, pivotable relation with the retaining structure and a lockedposition wherein the shank first surface is in direct frictionalengagement with the receiver second surface and the retaining structurethird surface; and d) the second surface of the receiver and the thirdsurface of the retainer cooperating to receive the first surface of theshank capture structure to allow polyaxial rotation of the shankrelative to the receiver in the unlocked configuration during assembly.2. The assembly of claim 1 wherein the shank upper portion has an uppercurved dome surface that extends into a rod-receiving channel in thereceiver to directly engage a rod in the rod-receiving channel.
 3. Theassembly of claim 1 wherein the first surface of the shank upper portionslidably matingly engages the second surface of the receiver cavity inthe unlocked position.
 4. The assembly of claim 1 wherein the shankupper portion has a top rounded surface for engagement with a rod. 5.The assembly of claim 4 wherein the shank upper portion further includesa substantially flat upper surface and an edge disposed between the flatupper surface and the rounded surface, each of the rounded surface, theflat surface and the edge sized and shaped for engagement with the rod.6. The assembly of claim 1 wherein the shank upper portion has a toolengagement formation disposed thereon adapted for non-slip engagement bya tool for driving the bone screw shank into bone.
 7. The assembly ofclaim 6 wherein the tool engagement formation is an axial projectionhaving a hexagonal profile.
 8. The assembly of claim 6 wherein the toolengagement formation is an internal driving feature.
 9. The assembly ofclaim 8 wherein the driving feature has a hexagonal profile.
 10. Theassembly of claim 1 wherein the retaining structure further comprisesfirst and second spaced ends, the retaining structure being compressibleand expandible with the first and second ends being movable toward andaway from one another.
 11. The assembly of claim 1 wherein the retainingstructure is bottom-loadable into the receiver.
 12. The assembly ofclaim 1 wherein the bone screw shank has a body for fixation to bone,the shank body being integral with the shank upper portion.
 13. Theassembly of claim 1 wherein the bone screw shank is cannulated.
 14. Theassembly of claim 1 further comprising a closure structure with a lowerend and that is insertable into the receiver so as to engage the rod andapply a downward force to the rod, the closure structure for operablyurging the bone screw shank through the rod in a direction tofrictionally lock the position of the shank upper portion with respectto the retaining structure and the receiver, thereby locking the shankin a selected angle with respect to the receiver.
 15. The assembly ofclaim 14 wherein: (a) the receiver arms each have a guide andadvancement structure on inside surfaces thereof; and (b) the closurestructure is sized and shaped to be positionable between the arms forclosing the channel, the closure structure having a splay-resistantguide and advancement structure for rotatably mating with the guide andadvancement structures on the arms, biasing the closure structure uponadvancement rotation against a rod disposed in the channel.
 16. Theassembly of claim 14 wherein the closure structure is adapted tooperably urge the rod against the shank upper portion upon the closurestructure being positioned in the receiver.
 17. The assembly of claim 1wherein the receiver defines a recess for receiving and retaining theretaining structure within the receiver cavity.
 18. The assembly ofclaim 17 wherein the recess is a circumferential groove.
 19. In apolyaxial bone screw assembly for surgical implantation, the assemblyincluding a rod receiver and a shank swivelable with respect to thereceiver, the improvement wherein: a) the shank is bottom-loadable intothe receiver and has an integral upper portion with a first convexsurface with a first radius that is sized and shaped for direct contactwith the rod to receive direct downward force from direct engagementwith the rod; the shank having a second lower convex surface forpolyaxial contact with the receiver and having a second radius that islarger than the first radius; and further comprising b) the receiverhaving a lower groove and a retaining structure that is outwardly biasedand received within the receiver groove for retaining the shank upperportion in a cavity in the receiver, the cavity being sized and shapedto allow polvaxial movement of the shank relative to the receiver duringpositioning of the shank, wherein when assembled the retaining structureis located at a lower end of the shank upper portion so as to directlyengage the shank and the rod frictionally engageable therewith when arod is positioned above the shank upper portion and applies a directdownward locking force to the shank upper portion and not to theretaining structure, so as to frictionally engage the retainingstructure and the shank.
 20. The assembly according to claim 19 wherein:a) the shank upper portion having a lower convex partially sphericallyshaped surface that is sized and positioned such that, when the shank isassembled in the receiver, the shank upper portion pivots within theretaining structure when the assembly is in a positioning configurationand frictionally engages the retaining structure when the assembly is ina locking configuration.
 21. The assembly according to claim 20 wherein:a) when the assembly is in a locking configuration the shank receives adownward force from the rod.
 22. A medical implant comprising: a) areceiver having a cavity, a lower portion with a lower opening, a lowergroove near the lower opening within the cavity and an upper portionwith a rod-receiving channel; b) a bone screw shank having an upperportion structured for up-loading through the receiver lower openinginto the cavity; the upper portion including a lower convex surface thatis sized and shaped to polyaxially rotate relative to the receiverduring positioning and that has a first radius; the upper portion havinga second convex surface that is adapted to engage a rod in the channeland that has a second radius smaller than the first radius; c) aretaining member securable to the receiver at a lower end of the shankupper portion by positioning in the groove, the retaining member beingsized and shaped for preventing the shank upper portion from passing outof the receiver through the lower opening; and d) a rod positionablewithin the rod receiving channel, the rod directly contacting andapplying a direct downward force only on the shank upper portion foroperably locking the shank in a position relative to the receiver. 23.The assembly according to claim 22 wherein: a) the shank extends into arod-receiving channel in the receiver so as to receive downward forcedirectly from the rod.
 24. A polyaxial bone screw assembly comprising:a) a bone screw shank having an upper portion; b) a receiver having a anupper rod channel adapted to receive a rod lower cavity with an innerspherical surface and a lower groove; the cavity being sized and shapedto allow polyaxial movement of the shank relative to the receiver duringpositioning of the shank; c) a retainer positioned within the groove insaid receiver cavity and having an inner spherical surface complimentaryto that of the receiver cavity spherical surface, such that saidspherical surfaces are substantially continuous and contiguous when saidretainer is coupled to said receiver, so as to hold said shank upperportion within said cavity and thereby allow polyaxial motion betweensaid shank and said cooperating receiver and retainer duringpositioning; and d) the shank being uploaded into the receiver cavityand extending into the channel after the assembly is assembled so as tobe adapted to receive all downward locking force from the rod tofrictionally lock the position of the shank relative to the receiverduring use.
 25. A polyaxial bone screw assembly comprising: a) a bonescrew shank having an upper portion with a capture structure having alower convex partially spherically shaped surface with a first radiusand a second upper convex surface having a second radius smaller thanthe first radius; b) a receiver having a pair of arms forming a channel,the receiver also having a cavity with an interior surface and anopening to an exterior of the receiver opposite the pair of arms, thecavity communicating with the channel, the bone screw upper portionbeing received in the cavity through the opening; and c) a retainingstructure being receivable in the cavity and positionable within arecess in the cavity surface and held there by outward biasing of theretainer structure when the shank upper portion is in the receiver, theretaining structure being sized and shaped to retain the shank upperportion within the receiver cavity and hold the upper portion in spacedrelation from the cavity surface; the shank upper portion being sizedand shaped to extend above the retaining structure and receive directdownward force from direct forceful contact between the rod and theshank when the shank upper portion is retained in the cavity by theretaining structure so that the shank receives all downward force fromthe rod directly so as to lock the angular position of the receiverrelative to the shank in a locked position due to the direct forcefulcontact between the rod and the shank, the assembly having an unlockedposition wherein the shank upper portion is in sliding, pivotablerelation with the retaining structure and a locked position wherein theshank capture structure is in direct frictional engagement with theretaining structure.
 26. A polyaxial bone screw assembly comprising: a)a bone screw shank having an upper portion with a capture structurehaving a lower convex partially spherically shaped first surface with afirst radius and a top convex surface with a second radius smaller thanthe first radius; b) a receiver having a pair of arms forming a channel,the receiver also having a cavity adapted to receive and allow pivotalmovement of the shank first surface during positioning and an opening toan exterior of the receiver opposite the pair of arms, the cavitycommunicating with the channel, the bone screw upper portion beingreceived in the cavity through the opening; c) a retaining structurebeing receivable in a lower end of the cavity and held therein byoutward spring biasing of the retainer structure, the retainingstructure being sized and shaped to retain the shank upper portionwithin the receiver cavity, the shank upper portion being sized andshaped to extend above the retaining structure and receive all downwardforce from the rod by direct forceful contact between the rod and theshank when the shank upper portion is retained in the cavity by theretaining structure so as to lock the angular position of the receiverrelative to the shank in a locked position due to the direct forcefulcontact between the rod and the shank, the assembly having an unlockedposition wherein the shank upper portion is in sliding, pivotablerelation with the retaining structure and a locked position wherein theshank is in direct frictional locking engagement with the retainingstructure.
 27. A polyaxial bone screw assembly comprising: a) a bonescrew shank having an upper portion with a capture structure having alower convex partially spherically shaped surface with a first radiusand an upper convex surface with a second radius smaller than the firstradius; b) a receiver having a pair of arms forming a channel, thereceiver also having a cavity with an interior surface and an opening toan exterior of the receiver opposite the pair of arms, the cavitycommunicating with the channel, the bone screw upper portion beingreceived in the cavity through the opening; and c) a retaining structurebeing receivable in a lower end of the cavity and secured therein byoutward spring biasing of the retaining structure, the retainingstructure being positioned within a recess in the cavity surface andhaving a non-pivotal relation with respect to the receiver, theretaining structure being sized and shaped to retain the shank upperportion within the receiver cavity and hold the upper portion in spacedrelation from the cavity surface; the shank upper portion being sizedand shaped to extend above the retaining structure and receive directdownward force from direct forceful contact between a rod positioned inthe channel and the shank when the shank upper portion is retained inthe cavity by the retaining structure and the retaining structure beingspaced from the rod so that the downward force from the rod to the shanklocks the angular position of the receiver relative to the shank in alocked position due to the direct forceful contact between the rod andthe shank, the assembly having an unlocked position wherein the shankupper portion is in sliding, pivotable relation with the retainingstructure and a locked position wherein the shank capture structure isin direct frictional engagement with the retaining structure.
 28. Apolyaxial bone screw assembly comprising: a) a bone screw shank havingan upper portion with a capture structure having a lower convexpartially spherically shaped first surface with a first radius and a topconvex surface with a second radius smaller than the first radius; b) areceiver having a pair of arms forming a channel, the receiver alsohaving a cavity adapted to receive and allow pivotal movement of theshank first surface during positioning and an opening to an exterior ofthe receiver opposite the pair of arms, the cavity communicating withthe channel, the bone screw upper portion being uploaded and received inthe cavity through the opening; c) a retaining structure beingreceivable in a lower part of the cavity and held in position by anoutward biasing of the retaining structure, the retaining structurebeing sized and shaped to retain the shank upper portion within thereceiver cavity and to have a non-pivotal relation with respect to thereceiver, the shank upper portion being sized and shaped to extend abovethe retaining structure and receive direct downward force from directforceful contact between a rod positioned in the channel and the shankand the retaining structure being spaced from the rod when the shankupper portion is retained in the cavity by the retaining structure so asto lock the angular position of the receiver relative to the shank in alocked position due to the direct forceful contact between the rod andthe shank, the assembly having an unlocked position wherein the shankupper portion is in sliding, pivotable relation with the retainingstructure and a locked position wherein the shank is in directfrictional locking engagement with the retaining structure.
 29. Apolyaxial bone screw assembly comprising: a) a bone screw shank havingan upper portion with a capture structure having a lower convexpartially spherically shaped surface with a first radius and an upperconvex surface with a second radius; b) a receiver having a pair of armsforming a channel, the receiver also having a cavity with an interiorsurface and an opening to an exterior of the receiver opposite the pairof arms, the cavity communicating with the channel, the bone screw upperportion being received in the cavity through the opening; and c) aretaining structure being receivable in a lower portion of the cavity,positionable within a recess in the cavity surface and having anon-pivotal relation with respect to the receiver, the retainingstructure being sized and shaped to retain the shank upper portionwithin the receiver cavity and hold the upper portion in spaced relationfrom the cavity surface; the shank upper portion being sized and shapedto extend above the retaining structure and only receive a directdownward force when the shank upper portion is retained in the cavity bythe retaining structure so as to lock the angular position of thereceiver relative to the shank in a locked position and so that theretaining structure receives the locking force only through the shank,the assembly having an unlocked position wherein the shank upper portionis in sliding, pivotable relation with the retaining structure and alocked position wherein the shank capture structure is in directfrictional engagement with the retaining structure; wherein the firstand second radii are different.
 30. A polyaxial bone screw assemblycomprising: a) a bone screw shank having an upper portion with a capturestructure having a lower convex partially spherically shaped firstsurface with a first radius and a top convex surface with a secondradius; b) a receiver having a pair of arms forming a channel, thereceiver also having a cavity adapted to receive and allow pivotalmovement of the shank first surface during positioning and an opening toan exterior of the receiver opposite the pair of arms, the cavitycommunicating with the channel, the bone screw upper portion beingreceived in the cavity through the opening; c) a retaining structurebeing receivable and secured in a lower portion of the cavity, theretaining structure being sized and shaped to retain the shank upperportion within the receiver cavity and to have a non-pivotal relationwith respect to the receiver, the shank upper portion being sized andshaped to extend above the retaining structure so that only the shankupper portion receives a direct downward force when the shank upperportion is retained in the cavity by the retaining structure so as tolock the angular position of the receiver relative to the shank in alocked position, the assembly having an unlocked position wherein theshank upper portion is in sliding, pivotable relation with the retainingstructure and a locked position wherein the shank is in directfrictional locking engagement with the retaining structure; wherein thefirst radius is larger than the second radius.